So far, stents have been used to expand a diameter of the body lumen such as the blood vessel and keep it to the expanded luminal diameter. The stent may be expanded by various methods such as balloon dilation, self-expansion using a shape memory material, mechanical expansion, or the like. The most widely used method is the balloon dilation. In the balloon dilation, a stent is introduced into a desired site in the body together with a balloon catheter, expanded by inflation of balloon to dilate a diameter of the lumen, and retained at the dilated site even after removing the deflated balloon from the site. The stent generally comprises luminal diameter-holding portions for dilating and holding the diameter of the lumen such as blood vessel, and joint portions for connecting the luminal diameter-holding portions in the longitudinal direction of the stent, and the stent is adapted to keep its expanded shape after expansion.
Proposed stents comprising luminal diameter-holding portions and joint portions include, for example, a stent comprising plural cylindrical components which are separately expandable in the radial direction thereof and are connected to one another so as to align on a common axis (JP-H06-181993 A); a stent comprising a tubular member expandable in the radial direction, the tubular member being constituted by a plurality of elongated members intersecting with one another (JP S62-231657 A); a stent comprising at least two unitary wire-like circular members each bent to form a plurality of substantially straight, non-overlapping segments connected at axial bends; the at least two circular members having at least one pair of aligned axial bends; and the at least two circular members connected by at least one substantially rigid joint at least one pair of aligned axial bends (JP H08-155035 A); a stent formed of a tube having a patterned shape which has first and second meander patterns having axes extending in first and second directions (JP H10-503676 A); and a stent with an open structure comprising a plurality of open cylindrical segments, each segment being defined by an interconnected struts, the segment being interconnected at end portions thereof by a plurality of diagonal interconnecting elements (JP H11-505441 A).
These stents of the prior art have been improved to some extent, but they still put a load on the lumen such as the blood vessel in the vicinity of edges of the expanded stent, resulting in obstruction or stenosis of the lumen. Further, it can not be said that these stents have sufficient flexibility, and thus it is often difficult to insert the stent into the objective site if the lumen has a three-dimensionally meandering course. In addition, the stents may cause wounds in the blood vessel during insertion into the objective site. If there is a branched blood vessel at the inflated position, it is hardily difficult to form a lateral hole in the placed stent. Further, the stents have such a problem that the length of the stent is shortened by expansion, i.e., so-called shortening.